Maui3 - 8-11-2024 at 04:46
Hi!
I am quite unsure about this, so I thought I'd ask some people more knowledgeble then me.
Could sodium bisulfate be used as alternative for sulfuric acid for nitrations?
jackchem2001 - 8-11-2024 at 16:21
I would expect not as HCl is a stronger acid than NaHSO4 by pKa and I didn't have success with using HCl + KNO3. However, maybe there is a different
result with HCl + HNO3 or NaHSO4 + HNO3?
[Edited on 9-11-2024 by jackchem2001]
Monoamine - 11-11-2024 at 21:07
When you add nitric acid and sodium bisulfate this sets up an equilibrium between these two entities and sodium nitrate and sulfuric acid:
NaHSO4 + HNO3 <--> H2SO4 + NaNO3
However, since sulfuric acid is by far the strongest acid in this equation, the equilibrium will be heavily shifted to the left, meaning you will only
generate a very small amount of sulfuric acid this way.
Below is the mechanism for aromatic nitration. Note that the nitration is carried out by a nitronium ion, which is generated by nitric acid
deprotonating sulfuric acid. This step is only favouried because sulfuric acid is a much stronger acid than nitric acid and likely also because the
sulfur is in a relatively high oxydation state, as opposed to the Cl ion in hydrochloric acid (but correct me if this hypothesis is wrong). So, simply
because NaHSO4 is a relatively weak acid, this reaction is not favoured. You would need to add a very large excess of NaHSO4 to
shift the equilibrium above to the right, so your nitration (if it occurs at all) would likely be extremely slow.
